Remove lxc-verison, lxc-ps and lxc-netstat

lxc-ps and lxc-netstat have an unfortunate tendency to break every so
often, produce mostly unreadable output and should be replaced by a
lxc-attach call in 99% of the cases.

In an effort to cleanup the lxc-* namespace, I think those two should
go, so this patch gets rid of them as well as any reference to them in
our documentation.

I also think that lxc-version should disappear as it's only a one line
shell script printing the version string, so having a whole command just
for that seems to be a bit of a waste.

Instead, this patch introduces a new --version common option which all
binaries will automatically inherit and that'll print LXC_VERSION on
stdout and exit 0.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>